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	<div id="winchm_template_button"><A href="debugger_engine_api_overview.htm" title="Previous topic"><img id="winchm_template_prev" alt="Previous topic" src="../template2/btn_prev_n.gif" border="0"></a><A href="using_client_objects.htm" title="Next topic"><img id="winchm_template_next" alt="Next topic" src="../template2/btn_next_n.gif" border="0"></a></div>
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<A href="introduction6.htm">Debugging Tools for Windows (WinDbg, KD, CDB, NTSD)</A> &gt; <A href="debugging_resources.htm">Debugging Resources</A> &gt; <A href="debugger_engine_and_extension_apis.htm">Debugger Engine and Extension APIs</A> &gt; <A href="using_the_debugger_engine_api.htm">Using the Debugger Engine API</A> &gt; <A href="debugger_engine_api_overview.htm">Debugger Engine API Overview</A> &gt; </div>
	<div id="winchm_template_title">Interacting with the Engine</div>
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	<div id="winchm_template_content"><div id="mainSection"><h3><a id="commands_and_expressions"></a><a id="COMMANDS_AND_EXPRESSIONS"></a>Commands and Expressions</h3>
<p>The debugger engine API provides methods to execute commands and evaluate expressions, like those typed into WinDbg's <a href="#Bookmark1264">Debugger Command Window</a>.  To execute a debugger command, use <a href="#Bookmark387"><b>Execute</b></a>. Or, to execute all of the commands in a file, use <a href="#Bookmark388"><b>ExecuteCommandFile</b></a>.</p>
<p>The method <a href="#Bookmark386"><b>Evaluate</b></a> will evaluate expressions using the C++ or MASM syntax.  The syntax used by the debugger engine to evaluate expressions--such as in the <b>Evaluate</b> method--is given by <a href="#Bookmark480"><b>GetExpressionSyntax</b></a> and can be changed using <a href="#Bookmark487"><b>SetExpressionSyntaxByName</b></a> and <a href="#Bookmark486"><b>SetExpressionSyntax</b></a>.  The number of different syntaxes that are recognized by the debugger is returned by <a href="#Bookmark483"><b>GetNumberExpressionSyntaxes</b></a>, and their names are returned by <a href="#Bookmark481"><b>GetExpressionSyntaxNames</b></a>.</p>
<p>The type of value that is returned by <b>Evaluate</b> is determined by the symbols and constants used in the string that was evaluated.  The value is contained in a <a href="#Bookmark906"><b>DEBUG_VALUE</b></a> structure and can be cast to different types using <a href="#Bookmark381"><b>CoerceValue</b></a> and <a href="#Bookmark382"><b>CoerceValues</b></a>.</p>
<h3><a id="aliases"></a><a id="ALIASES"></a>Aliases</h3>
<p><i>Aliases</i> are character strings that are automatically replaced with other character strings when used in debugger commands and expressions.  For an overview of aliases, see <a href="#Bookmark1268">Using Aliases</a>.  The debugger engine has several classes of aliases.</p>
<p>The <i>fixed-name aliases</i> are indexed by number and have the names <b>$u0</b>, <b>$u1</b>, ..., <b>$u9</b>.  The values of these aliases can be set using the <a href="#Bookmark464"><b>SetTextMacro</b></a> method and can be retrieved using <a href="#Bookmark430"><b>GetTextMacro</b></a> method.</p>
<p>The <i>automatic aliases</i> and <i>user-named aliases</i> can have any name.  The automatic aliases are defined by the debugger engine and the user-named aliases are defined by the user through debugger commands or the debugger engine API.  To define or remove a user-named alias, use the <a href="#Bookmark474"><b>SetTextReplacement</b></a> method.  The <a href="#Bookmark471"><b>GetTextReplacement</b></a> method returns the name and value of an automatic alias or a user-named alias.  All the user-named aliases can be removed using the <a href="#Bookmark473"><b>RemoveTextReplacements</b></a> method.  The <a href="#Bookmark470"><b>GetNumberTextReplacements</b></a> method will return the number of user-name and automatic aliases; this can be used with <b>GetTextReplacement</b> to iterate over all these aliases. The <a href="#Bookmark472"><b>OutputTextReplacements</b></a> method will print a list of all the user-named aliases, including their names and values.</p>
<div class="alert"><b>Note</b>   if a user-named alias is given the same name as an automatic alias, the user-named alias will hide the automatic alias so that when retrieving the value of the alias by name, the user-named alias will be used.</div>
<div> </div>
<h3><a id="engine_options"></a><a id="ENGINE_OPTIONS"></a>Engine Options</h3>
<p>The engine has a number of options that control its behavior.  These options are listed in <a href="#Bookmark882"><b>DEBUG_ENGOPT_XXX</b></a>.  They are returned by <a href="#Bookmark397"><b>GetEngineOptions</b></a> and can be set using <a href="#Bookmark451"><b>SetEngineOptions</b></a>.  Individual options can be set using <a href="#Bookmark376"><b>AddEngineOptions</b></a> and unset using <a href="#Bookmark446"><b>RemoveEngineOptions</b></a>.</p>
<h3><a id="interrupts"></a><a id="INTERRUPTS"></a>Interrupts</h3>
<p>An interrupt is a way to force a break into the debugger or to tell the engine to stop processing the current command, for example, by pressing Ctrl+Break in WinDbg.</p>
<p>To request a break into the debugger, or to interrupt the debugger's current task, use <a href="#Bookmark456"><b>SetInterrupt</b></a>.  To check if there has been an interrupt, use <a href="#Bookmark406"><b>GetInterrupt</b></a>.</p>
<div class="alert"><b>Note</b>    When undertaking a long task from a debugger extension, it is recommended that the extension check <b>GetInterrupt</b> regularly and stop processing if an interrupt has been requested.</div>
<div> </div>
<p>When requesting a break into the debugger, the engine might time out if it takes too long for the target to carry out the break-in.  This can occur if the target is in a non-responsive state or if the break-in request is blocked or delayed by resource contention.  The length of time the engine will wait is returned by <a href="#Bookmark407"><b>GetInterruptTimeout</b></a> and can be set using <a href="#Bookmark457"><b>SetInterruptTimeout</b></a>.</p></div></div>	
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